Industrial installations in which vacuum pumps are used to evacuate work chambers, e.g. when reactive gases are pumped in the semiconductor industry, include evacuation ducts leading to the outside and connected to the outlets of the pumps. It is not possible to allow the pumping unit to deliver inside the factory, in particular because of the noxiousness of some of the pumped gases. It is therefore absolutely necessary to evacuate the exhaust gases to the outside. This is done via a duct that often contains a purification system referred to as a "Scrubber" system, and an extractor fan.
In order to dilute the pumped gases and so as to enable them to be evacuated more quickly at the outlet of the pump, the pumping unit, e.g. a multi-stage Roots pump, is equipped with a feed system for supplying an inert "purge" gas which is injected into the various ,stages of the pump. This enables improved evacuation of the above-mentioned condensates or particles, thereby protecting the inside of the pump. However, it does not prevent particles from being deposited in the evacuation duct whose cross-sectional area decreases over time with such deposition, thereby giving rise to excessive pressure at the outlet, which excessive pressure damages the pump. Furthermore, such particles also cause damage in the purification device, if there is such a device.